Heretofore, plastic films such as nylon, have been and still are widely used for debulking and autoclave curing operations in composites manufacture as for instance see U.S. Pat. No. 3,666,600 (Yoshino) issued May 3, 1972. The forming of the film to closely fit into the corners and contours of complex shaped parts, however, is labor intensive and the results are rather variable. The film is usually laid over the composite layup on the tool and then hand conformed to the tool shape, and sealed with chromate putty about its periphery to the tool. The completely bagged part and tool is then autoclaved. The film is not reusable and is thrown away. Parts formed using this conventional film system have had a large number of wrinkles, bridging, pinholes and leaks due to edge sealing problems, all of which have contributed to limit the productivity of the film sealing system.
U.S. Pat. No. 4,125,526 (McCready) issued Nov. 14, 1978 suggests using polyurethane for vacuum blankets on radar domes, i.e a relatively smooth surfaces. Liquid polyurethane precursor compounds are sprayed onto the uncured components for forming the radar dome. This structure is then allowed to stand for a period of time to allow for polymerization of the precursor compounds into a polyurethane blanket followed by autoclaving to cure the radar dome materials into the resultant radar dome.
Reusable silicone rubber membranes and mechanical seals to replace the film and chromate are known from U.S. Pat. No. 2,837,453 (Englehart) issued June 3, 1958, U.S. Pat. No. 3,382,125 (Laudermild) issued May 7, 1968 and U.S. Pat. No. 4,287,015 (Danner) issued Sept. 1, 1981 which teach the use of a flexible silicone rubber blanket vaccum secured about the perimeter of the tool. The teachings of these patents work well enough for use on tooling which is of relatively flat conformation but becomes less and less satisfactory as the shape of the part to be laminated becomes more complex and incorporates reentrant portions or recesses and tight radius inside contours.
The use of an unshaped, highly stretchable silicone rubber membrane which is brought down over the tool and drawn to it with a vacuum so that the membrane elasticity permits it to conform to the desired shape has also been tried, but has not been successful on highly contoured shapes since resin buildup is formed in the contoured areas. This has lead to wrinkling and puckering in production parts.
While it has been proposed to make molded silicone bags by spraying up or brushing a silicone suspension dispersed in a solvent over the tool to form a silicone mold therefrom, the use of such has been limited to a few production cycles due principally to shrinkage. While reinforcement with fiberglass has been suggested to obtain a greater number of production life cycles, the reduced flexibility and delamination of the bag has limited the application of this concept. For a brief discussion of the above concept see Dow Corning's New Product Information Bulletin entitled "Use of High Strength RTV Silicone Rubber in Contour Vacuum Bag Molding" (1983).
In general, a principal limitation of the above molded bag concept is found to result from continuing and progressive shrinkage during each subsequent autoclave cycle, particularly when used on tools of complex, highly contoured shaped.
In view of the above it is evident that there exists a need for improved methods and apparatus for bagging laminates of complex shape for debulking and autoclave curing purposes.